A conventional sealed fiber array for an optical transmission module is disclosed, for example, in JP-A-8-179171. In such a sealed fiber array, optical fibers are arranged in respective V grooves, and both ends of the fiber array are polished optically. The end of the fiber array to be exposed to outside of a package of the transmission module is capable of being connected to an optical connector.
To allow connection of such a package to the optical connector, it is necessary to provide one or more grooves for respective guide pins in a substrate of the sealed fiber array. In a traditional sealed fiber array having such V-grooves, the fiber grooves and the guide grooves extend from one end of the substrate to the other, so that guide holes extend through the sealed fiber array from its one end to the other. In this case, however, ambient air may enter into the package, through gaps between the guide holes and the guide pins. In a package in which one or more semiconductor elements such as laser diodes and/or photodiodes are provided, the elements tends to be degrade when exposed to ambient air.